The invention relates to an optical apparatus for deflecting or positioning a radiation beam relative to recording and reproducing tracks in an information carrier, which apparatus comprises an objective whose position relative to the information carrier can be corrected continually by means of an actuating device, which device comprises an adjustable objective support which is responsive in a magnetic field and stationary coils which adjust the objective support in the magnetic field by electrical energization.
For inscribing and reading rotating information-carrying discs the light beam must be aimed accurately at the desired track. This is effected by means of an electrical correction system which influences the objective support and thereby aims the focused light beam at the desired track.
Netherlands Patent Application 81 03 305 to which co-pending U.S. patent application Ser. No. 13,701, now U.S. Pat. No. 4,561,081, assigned to the assignee of the instant application, corresponds, describes an optical apparatus for deflecting or positioning a light beam, in which the write or read beam is incident on the record carrier perpendicularly to its surface at the correct location and at the correct instant. At the same time the objective is maintained at the correct distance from the record-carrier surface. This is achieved in that the write or read beam can be shifted along three mutually perpendicular axes and is also pivotable about two of these three axes. Thus the beam may be said to have five degrees of freedom.
For the correct positioning of the objective the objective is suspended so as to be freely movable and forces for the movements along or about the five axes are applied by means of a plurality of actuators.
These actuators comprise coils which produce magnetic fields which position the objective correctly. One of the optical apparatuses described employs nine actuators in total, comprising five permanent magnets and nine coils. The permanent magnets of all the nine actuators are arranged on the movable objective support. All the systems can be actuated simultaneously.
The use of five permanent magnets to be mounted on the objective support in the correct position and the necessity of providing nine actuators render the optical apparatus mechanically and electrically intricate.